a(n) is the smallest k such that A316506(k) = n.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =20a(5) =40a(6) =120a(7) =520a(8) =1560a(9) =8840a(10) =26520a(11) =185640a(12) =769080a(13) =5383560a(14) =28455960a(15) =199191720a(16) =1166694360a(17) =8166860520a(18) =61834801080a(19) =432843607560